Development of efficient electric motor drives for vehicles, with improved electronic control systems and portable power sources, has drawn increasing attention as a viable alternative or adjunct to combustion engine drives. For example U.S. Pat. No. 6,492,756 to Maslov et al. and U.S. Pat, No. 6,617,746 to Maslov et al. describe motor structures that provide high torque output capability with minimum power consumption, thus especially suitable to electric vehicle propulsion. Electromagnets are used as isolated magnetically permeable structures configured in a stator annular ring. FIG. 1 is a plan view of a motor such as described in the U.S. Pat. No. 6,492,756. Rotor member 20 is an annular ring structure having permanent magnets 22 substantially evenly distributed along cylindrical back plate 24. The permanent magnets are rotor poles that alternate in magnetic polarity along the inner periphery of the annular ring. The rotor surrounds a stator member 30, the rotor and stator members being separated by an annular radial air gap. Stator 30 comprises a plurality of electromagnet core segments of uniform construction that are evenly distributed along the air gap. Each core segment comprises a generally u-shaped magnetic structure 36 that forms two poles having surfaces 32 facing the air gap. The poles of each core segment are aligned in a direction that is perpendicular to the axis of rotation of the motor. The legs of the pole pairs are wound with windings 34, although the core segment may he constructed to accommodate a single winding formed on a portion linking the pole pair. Each stator electromagnet core structure is separate, and magnetically isolated, front adjacent stator core elements. The stator elements 36 are secured to a non-magnetically permeable support structure, thereby forming an annular ring configuration.
FIG. 2 is a partial three dimensional perspective view of a motor such as described in the U.S. Pat. No. 6,617,746. The poles 32 of each core segment are aligned in a direction parallel to the axis of rotation. The stator core segments are rigidly secured to plates 42, only one of which is shown in the drawing. The plates are affixed to a stationary shaft 38 in a manner more particularly described in the patent. An annular ring is thus formed of stator core segments that are coextensively aligned in the axial direction across the air gap from the rotor. The annular rotor backplate and attached permanent magnets are secured to housing 40, which is journalled to the shaft on the outside of the plates through appropriate bushings and bearings.
Isolation of the electromagnet groups in the above described configurations permits individual concentration of flux in the magnetic cores of the groups, with virtually no flux loss or deleterious transformer interference effects with other electromagnet members. Operational advantages are gained from this segmented electromagnetic architecture. Magnetic path isolation of an individual pole pair from other pole groups eliminates a flux transformer effect on an adjacent group when the energization of the pole pair windings is switched.
As discussed in the above identified patents, there is significant incentive to increase the torque and power density of a machine by improving the architectural configuration if the stator and rotor constituents. Magnetic circuit topologies have been developed that promote significant weight reduction in the magnetic mass, as well as gain improvement of the form factor of the magnetic design. Related U.S. Pat. No. 6,717,323 to Soghomonian describes benefits to be gained from utilization of three dimensional aspects of motor structure. Advantages are recognized from the use of materials such as a soft magnetically permeable medium that is amenable to formation of a variety of particular shapes. For example, core material may be manufactured from soft magnet grades of Fe, SiFe, SiFeCo, SiFeP powder material, each of which has a unique power loss, permeability and saturation level. Core geometries and core dimensions of stator elements, with relevant tolerances, can be fabricated without the need to form laminations. The magnetic potential gradient developed between coupled poles of rotor permanent magnets and stator electromagnets thus can he optimized. Copending U.S. patent application Ser. No. 10,761,305 of Soghomonian, filed Jan. 22, 2004 and entitled “Soil Magnetic Composites,” discloses the manufacture of machine cores of soft magnetically permeable materials. The disclosure of that application is hereby incorporated by reference in the present description.
Electric traction systems demand high torque from low voltage propulsion units. The low voltage restriction satisfies a need to conserve space by minimizing the number of battery cells and eliminating extra insulation that otherwise would be required for high voltage protection. In order to deliver high torque from a low voltage source, it is necessary to draw high current through the motor windings. High current operation can produce excess heat, which must be eliminated to maintain efficient continuous operation and to avoid damage to the motor. A thermal management system is needed that can maintain machine operation within thermal limits. Such a system should be of light weight, and capable of installation in various motor topologies. Classical issues concerning copper, hysteresis and excess eddy current losses tend to dictate the need for new cooling methods. Machines commonly have either a cooling jacket embedded in its external housing or internally placed heat exchangers, possibly with liquid cooling ducts. In machines with laminated stator cores, there is little freedom for shaping cooling paths. Liquid cooling systems, which require pressurized coolant to be channeled through ducts or cooling jackets, have inherent risks. Excess pressure can cause leaks of the cooling fluid; poor sealing of joints could cause electrical shorts in the machine, as well as localized galvanic corrosion and erosion of the machine elements.
Commonly assigned copending U.S. application of Matin et al., application Ser. No. 10/893,878, filed Jul. 20, 2004 and entitled “Dynamoelectric Machine With Embedded Heat Exchanger,” describes cooling systems for a motor that is particularly useful as a submersible solid shaft pump motor. The motor is enclosed in a sealed housing within which air can be circulated through the machine components for contact with one or more sealed containers. The sealed container, known as a “heat pipe,” encloses a coolant medium, such as water. The pipe is lined with a porous “wick structure.” The wick is saturated with a proper amount of working fluid. The atmosphere inside the heat pipe is set by an equilibrium of liquid and vapor. As heat enters an evaporator portion of the heat pipe, this equilibrium is upset and vapor is generated at a slightly higher pressure. The higher pressure vapor travels to a condenser end portion of the heat pipe where the slightly lower temperatures cause the vapor to condense giving up its latent heat of vaporization. The condensed fluid is then pumped back to the evaporator by the capillary forces developed in the wick structure.
The machine housing structure of the copending Matin application includes a central portion that includes the stator and rotor elements, and a cavity longitudinally adjacent the central portion in which a plurality of heat pipes are mounted. The heat pipes extend through the housing to external ends that are attached to cooling fins to facilitate heat transfer from the heat pipes to the external environment. The heat pipes provide heat transfer from the air circulated through the motor. Heat absorbed in the evaporating sections causes fluid to boil to the vapor phase. Thermal energy is released at the condensing sections to the cooling fins that dissipate heat away from the heat pipes.
The cooling system of the Matin et al. application is positioned in a relatively large structure that is not particularly constrained by space and weight considerations. The advantages described in the Matin et al. application would be beneficial for machines in vehicle traction drives, for example, wherein appropriate thermal management of SMC cores is essential for satisfactory operation. Such a cooling system should be readily amenable to installation in the immediate vicinity of the source of heat generation while conserving space and weight of the machine.